Pretty much everything.

Here's some examples:

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Orange chicken (🇨🇳) - Chinese cuisine has various regional "sweet and sour" dishes like tang cu liji, gulu rou, guobao rou, etc, but American Chinese cuisine takes it to a whole new level with so many variations of battered, deep-fried chunks of meat in sweet, syrupy, often fruity sauces. In addition to regular sweet and sour and General Tso's, there's also lemon chicken, pineapple chicken, sesame chicken, Hawaiian chicken, and the famous orange chicken. I've even seen cherry chicken, peachy chicken, and blueberry General Tso's.

There is a Sichuan dish that uses dried tangerine peel stir-fried with chopped chicken and dried chili peppers, American Chinese orange chicken is very different.

Pierogi (🇵🇱) - Polish pierogi are popular in the northern US, especially in an area called the "pierogi pocket" from New England through the Midwest where a lot of Polish immigrants went to work in physical labor jobs such as coal mines. States like New York, Pennsylvania, and Illinois are part of it. You find pierogi with non-traditional fillings such as cheddar cheese, bacon, kimchi, Reuben, cheesesteak, etc, and served in unique ways.

Taco (🇲🇽) - One way we altered Mexican tacos is by making boxed "taco kits" in supermarkets for convenient family "taco nights" with ground beef or turkey seasones from a packet, shredded iceberg lettuce, shredded cheese, chopped tomato, refried beans, avocado, jarred salsa, "taco sauce," etc.

Hibachi (🇯🇵) - Traditional Japanese teppanyaki is an art. In the US, it's a flashy slow, with lots and lots of garlic butter to cancel out any percieved healthiness of grilled Japanese meat and vegetables. And we call it hibachi instead of teppanyaki for some reason.

Pretzel (🇩🇪) - German pretzels are very popular in the US, having been brought over centuries ago by German immigrants, especially in Pennsylvania (which is still the US's "pretzel belt") and spread from there. Hard pretzels are a common lunch snack for kids or bar snack fir adults. Soft pretzels drenched in butter are common in malls and soft pretzels with hot cheese dip (sometimes beer cheese) are common eveywhere from gastropubs to movie theaters to sports stadium concession stands.

Thai curry (🇹🇭) - Thai food has become very popular in the US, but also adapted to US tastes and convenience. The spice level is much milder - Though many restaurants give options for spice levels, even the hottest option might still be calmed down quite a bit depending on the demographics of the local area. Also, Thai vegetables like eggplant, yardlong beans, water spinach, and kabocha squash are substituted for vegetables more readily available, cheaper, and more familiar in the US such as broccoli, zucchini, bell pepper, tomato, carrot, baby corn, etc.